An optical unit such as a cellular phone having an imaging device is known as an example including a lens fitted in a lens barrel (see JP-A-2004-4566 (FIG. 2)).
The lens used in such an optical unit is often a plastic lens formed from a plastic material by injection molding, which is a method suitable for mass production. As shown in FIG. 6, the molding of such a plastic lens is carried out by injecting a plastic material into a cavity 104 defined between a stationary mold 101 having a stationary core 100 for giving an accurate finish to the convex side of a lens and a movable mold 103 having a movable core 102 for giving an accurate finish to its concave side, whereby a plastic lens 1 as shown in FIG. 7 is molded. It has been the case that the plastic lens 1 as molded has a protrusion (e.g., a burr) 1A formed between the molds 101 and 103, as shown in FIG. 8. This is unavoidable due to the construction of the molds.
The protrusion 1A is unavoidably formed on the plastic lens 1, as stated above, and when that portion is not taken into consideration in designing a lens barrel, it is likely that a diametrical force may act on the lens and cause axial deviation or strain inside the lens, thereby lowering its optical performance.